But if it's being done deliberately, even if we figure out the real
address they can just re-subscribe with another alias.

If someone wanted to annoy everybody deliberately, there are much much
better ways of doing it.

Or they could start an email thread about being upset over someone
having an anonymous autoresponder on a mailing list. ;o)
/me runs
--
Mike A. Harris * Open Source Advocate * http://mharris.ca
Proud Canadian.